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Elevation-dependent influence of snow accumulation on forest greening

Abstract

Rising temperatures and declining water availability have influenced the ecological function of mountain forests over the past half-century. For instance, warming in spring and summer and shifts towards earlier snowmelt are associated with an increase in wildfire activity and tree mortality in mountain forests in the western United States1,2. Temperature increases are expected to continue during the twenty-first century in mountain ecosystems across the globe3,4, with uncertain consequences. Here, we examine the influence of interannual variations in snowpack accumulation on forest greenness in the Sierra Nevada Mountains, California, between 1982 and 2006. Using observational records of snow accumulation and satellite data on vegetation greenness we show that vegetation greenness increases with snow accumulation. Indeed, we show that variations in maximum snow accumulation explain over 50% of the interannual variability in peak forest greenness across the Sierra Nevada region. The extent to which snow accumulation can explain variations in greenness varies with elevation, reaching a maximum in the water-limited mid-elevations, between 2,000 and 2,600 m. In situ measurements of carbon uptake and snow accumulation along an elevational transect in the region confirm the elevation dependence of this relationship. We suggest that mid-elevation mountain forest ecosystems could prove particularly sensitive to future increases in temperature and concurrent changes in snow accumulation and melt.

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Figure 1: Study area and correspondence between SWE and NDVI across the Sierra Nevada Mountains.
Figure 2: Relationships between forest greenness and maximum snow accumulation on a regional basis.
Figure 3: Relationships between forest greenness and maximum snow accumulation across elevations.
Figure 4: In situ measurements of GEE and snow accumulation in the southern Sierra Nevada Mountains.

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Acknowledgements

This research was supported by NSF EAR-1032295, NSF EAR-1032308, NSF EAR-0619947, the Southern Sierra Critical Zone Observatory (NSF EAR-0725097), NASA-NNX08AH18G and the Jet Propulsion Laboratory Research and Technology Development Fund. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA. We thank F. Gehrke for facilitating access to the California Department of Water Resources snow sensor data, M. Meadows and G. Winston for assistance in the field, and T. Veblen and M. Williams for comments on the manuscript and useful discussions.

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Contributions

E.T. jointly conceived the study and designed the analyses with N.P.M. E.T. collected and performed the data analyses of NDVI and SWE. E.T. and N.P.M. carried out interpretation of results jointly, and E.T. prepared the initial manuscript. M.L.G., A.E.K. and R.C.B. provided the GEE data, and contributed with interpretations of the GEE and SWE measurements and the corresponding text. E.T. and N.P.M. edited the final version of the manuscript.

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Correspondence to Ernesto Trujillo.

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The authors declare no competing financial interests.

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Trujillo, E., Molotch, N., Goulden, M. et al. Elevation-dependent influence of snow accumulation on forest greening. Nature Geosci 5, 705–709 (2012). https://doi.org/10.1038/ngeo1571

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